static extern int ExternalIoCtl(int fd, uint request, ref spi_ioc_transfer xfer);
/// +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=
/// <summary>
/// Writes/Reads a buffer out/in to/from an SPI Slave Device.
///
/// Note that the TO/FROM's and IN/OUT's in the above line are there because
/// the SPI protocol always reads a byte for every byte sent. If you send a
/// byte you get a byte. If you do not sent a byte you will never receive
/// a byte since this code operates as an SPI Master. Thus if you only
/// wish to receive you must send an equivalent number of bytes. The
/// bytes you send are determined by the Slave. Sometimes this is just
/// 0x00 and sometimes it represents an address to read - exactly what you,
/// send is entirely slave device implementation dependent.
///
/// If you only wish to transmit, not receive, just use NULL for your
/// rxBuffer. The SPI port will still receive, of course, but you will
/// not be bothered by it.
///
/// NOTE: the Slave Select is set when you opened the port. The rule is
/// one slave to one SPISlaveDeviceHandle.
///
/// </summary>
/// <param name="ssHandle">The SPI Slave Device handle to write to</param>
/// <param name="txByteBuf">The buffer with bytes to write</param>
/// <param name="rxByteBuf">The buffer with bytes to receive. Can be NULL</param>
/// <param name="numBytes">The number of bytes to send/receive
/// <history>
/// 01 Dec 16 Cynic - Originally written
/// </history>
public void SPITransfer(SPISlaveDeviceHandle ssHandle, byte[] txByteBuf, byte[] rxByteBuf, int numBytes)
{
int spiFileDescriptor = -1;
int ioctlRetVal = -1;
// sanity check
if (ssHandle == null)
{
throw new Exception("Null Slave Device Handle");
}
if (txByteBuf == null)
{
throw new Exception("Null tx buffer");
}
if (numBytes <= 0)
{
throw new Exception("numBytes <= 0");
}
// set up our file descriptor
// are we an internal chip select type slave device?
if ((ssHandle.SPISlaveDevice == SPISlaveDeviceEnum.SPI_SLAVEDEVICE_CE0) ||
(ssHandle.SPISlaveDevice == SPISlaveDeviceEnum.SPI_SLAVEDEVICE_CE1))
{
// yes we are, just use this descriptor
spiFileDescriptor = ssHandle.SpiDevFileDescriptor;
}
else if (ssHandle.SPISlaveDevice == SPISlaveDeviceEnum.SPI_SLAVEDEVICE_GPIO)
{
if (ssHandle.GpioSlaveSelect == null)
{
throw new Exception("No GPIO Slave Select device found.");
}
// use the descriptor of the first non-GPIO slave select
// we find.
// get first slave device. We need the file descriptor
SPISlaveDeviceHandle firstHandle = GetFirstSlaveDeviceWithFD();
// sanity check
if (firstHandle == null)
{
throw new Exception("At least one non GPIO Slave Device must be enabled.");
}
// use this descriptor
spiFileDescriptor = firstHandle.SpiDevFileDescriptor;
}
else
{
// should never happen
throw new Exception("unknown slave device type");
}
// the data needs to be in unmanaged global memory
// so the spidev driver can see it. This allocates
// that memory. We MUST release this!
IntPtr txBufPtr = Marshal.AllocHGlobal(numBytes + 1);
IntPtr rxBufPtr = Marshal.AllocHGlobal(numBytes + 1);
try
{
// copy the data from the tx buffer to our pointer
Marshal.Copy(txByteBuf, 0, txBufPtr, numBytes);
// create and fill in the contents of our transfer struct
spi_ioc_transfer xfer = new spi_ioc_transfer();
xfer.tx_buf = txBufPtr;
xfer.rx_buf = rxBufPtr;
xfer.len = (UInt32)numBytes;
xfer.speed_hz = (UInt16)ssHandle.SpeedInHz;
xfer.delay_usecs = ssHandle.DelayUSecs;
xfer.bits_per_word = ssHandle.BitsPerWord;
xfer.cs_change = ssHandle.CSChange;
xfer.pad = 0;
if (ssHandle.SPISlaveDevice == SPISlaveDeviceEnum.SPI_SLAVEDEVICE_GPIO)
{
// lower the slave select
ssHandle.GpioSlaveSelect.Write(false);
try
{
// this is an external call to the libc.so.6 library
ioctlRetVal = ExternalIoCtl(spiFileDescriptor, SPI_IOC_MESSAGE_1, ref xfer);
}
finally
{
// 06 Dec 16 - bug here was (false)
// raise the slave select
ssHandle.GpioSlaveSelect.Write(true);
}
}
else
{
// this is an external call to the libc.so.6 library
ioctlRetVal = ExternalIoCtl(spiFileDescriptor, SPI_IOC_MESSAGE_1, ref xfer);
}
// did the call succeed?
if (ioctlRetVal < 0)
{
// it failed
throw new Exception("ExternalIoCtl on device " + ssHandle.SPISlaveDevice + " failed. retval=" + ioctlRetVal.ToString());
}
// did the caller supply a receive buffer
if (rxByteBuf != null)
{
// yes they did, copy the returned data in
Marshal.Copy(rxBufPtr, rxByteBuf, 0, numBytes);
}
}
finally
{
// Free the unmanaged memory.
Marshal.FreeHGlobal(txBufPtr);
Marshal.FreeHGlobal(rxBufPtr);
}
}